Humidex / Heat Index Reference for Motorcycle Riders

Hydrate for the humidex, not the air temperature.

Humidex (called "heat index" in the United States) is how hot the air feels once you factor in humidity. When the air is humid, your sweat cannot evaporate fast enough to cool you, so your body stays hotter than the thermometer reading suggests.

For motorcycle riders, this matters even more. You are working hard in protective gear, and the wind that normally cools you at 25°C / 77°F does almost nothing once the air temperature climbs near body temperature. Heat exhaustion sneaks up.

Two charts below cover the unit systems endurance riders use:

Metric: °C vs humidity (Canada, Europe, UK, Australia, New Zealand, most of the world)
US: °F vs humidity (United States)

Find the air temperature on the top, find the humidity on the left, and the number in the cell is what the heat feels like. Dress, hydrate, and pace for that number.

Values use the Canadian Humidex formula (Environment Canada), which stays meaningful at extreme combinations of temperature and humidity. The US "heat index" formula is mathematically the same idea but tends to extrapolate to unrealistic numbers above 40°C / 104°F, so we use Humidex for accuracy.

Note on the cool corner of the chart: humidex is officially defined only when air is 27°C / 80°F or warmer. Below that threshold, the cell shows the air temperature unchanged, since there is no meaningful heat amplification. For cold weather, use the Wind Chill Reference instead.

Comfortableup to 28°C / 82°F

Slight discomfort29-34°C / 84-93°F

Discomfort35-39°C / 95-102°F

Avoid exertion40-45°C / 104-113°F

Dangerous to ride46°C+ / 115°F+

Metric: °C vs Relative Humidity

RH ↓ Temp →	27°C	28°C	29°C	30°C	31°C	32°C	33°C	34°C	35°C	36°C	37°C	38°C
40%	29	31	32	34	35	37	39	40	42	44	46	47
45%	30	32	34	35	37	38	40	42	44	46	47	49
50%	31	33	35	36	38	40	42	43	45	47	49	51
55%	32	34	36	38	39	41	43	45	47	49	51	53
60%	33	35	37	39	41	43	44	46	49	51	53	55
65%	34	36	38	40	42	44	46	48	50	52	55	57
70%	35	37	39	41	43	45	47	50	52	54	56	59
75%	36	38	40	42	45	47	49	51	53	56	58	61
80%	38	40	42	44	46	48	50	53	55	58	60	63
85%	39	41	43	45	47	49	52	54	57	59	62	65
90%	40	42	44	46	48	51	53	56	58	61	64	67
95%	41	43	45	47	50	52	55	57	60	63	66	69
100%	42	44	46	49	51	54	56	59	62	65	68	71

US: °F vs Relative Humidity

RH ↓ Temp →	78°F	80°F	82°F	84°F	86°F	88°F	90°F	92°F	94°F	96°F	98°F	100°F
40%	78	80	87	90	93	96	99	103	106	109	113	117
45%	78	80	89	92	95	99	102	105	109	112	116	120
50%	78	80	91	94	97	101	104	108	112	115	119	123
55%	78	80	93	96	100	103	107	111	114	118	123	127
60%	78	80	95	98	102	106	109	113	117	121	126	130
65%	78	80	97	100	104	108	112	116	120	125	129	134
70%	78	80	98	102	106	110	114	119	123	128	132	137
75%	78	80	100	104	108	113	117	121	126	131	135	141
80%	78	80	102	106	111	115	119	124	129	134	139	144
85%	78	80	104	108	113	117	122	127	132	137	142	147
90%	78	80	106	111	115	120	124	129	134	140	145	151
95%	78	80	108	113	117	122	127	132	137	143	149	154
100%	78	80	110	115	119	124	130	135	140	146	152	158

What humidex means for riding

Humidex categories tuned for motorcyclists in protective gear:

Slight discomfort (yellow, 29-34°C / 84-93°F): noticeable but manageable. Drink more water than usual, pace yourself, take breaks.
Discomfort (orange, 35-39°C / 95-102°F): fatigue builds faster, sweat does not cool as well. Shorten ride legs, hydrate at every fuel stop, watch for early signs of heat illness.
Avoid exertion (red, 40-45°C / 104-113°F): heat cramps and heat exhaustion likely. Riding in full motorcycle gear in this zone is risky regardless of conditioning. Consider postponing or shifting to cooler hours.
Dangerous to ride (dark red, 46°C+ / 115°F+): heat stroke risk is real. This is not the day for an endurance ride. Postpone, wait for a cooler window.

Why wind does not save you in hot, humid air

The body's main cooling mechanism above body temperature (37°C / 99°F) is sweat evaporation. Wind helps evaporation up to a point, but only if there is room for the water to evaporate. When humidity is high, the air is already saturated and your sweat just sits on your skin. Wind brings more hot, humid air across you faster, which can actually increase heat gain at very high temperatures.

This is why humidex uses humidity, not wind speed, as its second variable. For motorcycle riding, the humidex reading tells you what your body actually has to deal with regardless of how fast you are moving.

What this means for endurance riding

A 24-hour ride that starts at 30°C / 86°F with 80% humidity sits in the orange band (extreme caution) for most of the daylight hours. The same temperature at 40% humidity sits in yellow (caution). Same air temperature, different danger levels.

Before a long summer ride, check both temperature AND humidity forecasts. A "hot day" with low humidity is manageable. A "hot day" with high humidity is a different ride entirely.

For more on hot-weather endurance riding strategy, see Endurance Riding in Heat.